191 research outputs found
Electron acceleration in vacuum by ultrashort and tightly focused radially polarized laser pulses
Exact closed-form solutions to Maxwell's equations are used to investigate
electron acceleration driven by radially polarized laser beams in the
nonparaxial and ultrashort pulse regime. Besides allowing for higher energy
gains, such beams could generate synchronized counterpropagating electron
bunches.Comment: 3 pages, 3 figures. To appear in the proceedings of the Ultrafast
Phenomena XVIII conferenc
Orientational dynamics in supercooled glycerol computed from MD simulations: self and cross contributions
The orientational dynamics of supercooled glycerol using molecular dynamics
simulations for temperatures ranging from 323 K to 253 K, is probed through
correlation functions of first and second ranks of Legendre polynomials,
pertaining respectively to dielectric spectroscopy (DS) and depolarized dynamic
light scattering (DDLS). The self, cross, and total correlation functions are
compared with relevant experimental data. The computations reveal the low
sensitivity of DDLS to cross-correlations, in agreement with what is found in
experimental work, and strengthen the idea of directly comparing DS and DDLS
data to evaluate the effect of cross-correlations in polar liquids. The
analysis of the net static cross-correlations and their spatial decomposition
shows that, although cross-correlations extend over nanometric distances, their
net magnitude originates, in the case of glycerol, from the first shell of
neighbouring molecules. Accessing the angular dependence of the static
correlation allows us to get a microscopic understanding of why the rank-1
correlation function is more sensitive to cross-correlation than its rank-2
counterpart.Comment: 9 pages, 6 figure
The chemistry of bromine in the stratosphere: Influence of a new rate constant for the reaction BrO + HO2
The impact of new laboratory data for the reaction BrO + HO2 yields HOBr + O2 in the depletion of global stratospheric ozone has been estimated using a one-dimensional photochemical model taking into account the heterogeneous reaction on sulphate aerosols which converts N2O5 into HNO3. Assuring an aerosol loading 2 times as large as the 'background' and a reaction probability of 0.1 for the above heterogeneous reaction, the 6 fold increase in the measured rate constant for the reaction of BrO with HO2 increases the computed depletion of global ozone produced by 20 ppt of total bromine from 2.01 percent to 2.36 percent. The use of the higher rate constant increases the HOBr mixing ratio and makes the bromine partitioning and the ozone depletion very sensitive to the branching ratio of the potential channel forming HBr in the BrO + HO2 reaction
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